let pic = document.querySelector('.pic');
console.log(pic.className); //图片起的名字
console.log(pic.innerHTML); //图片的内容
console.log(pic.title);     //图片的标题

let btn = document.querySelector('.btn');
btn.onclick = function () {
    pic.src = '../image/12.jpg';
    pic.style.width = '300px'
}

let btn1 = document.querySelector('.btn1');
let i = 0;
btn1.onclick = function () {
    i++;
    //找到box div
    let box = document.querySelector('.box');
    box.innerHTML = i + '.hello world!<br/>'
}